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WELLESLEY, Mass. - As a new astronomy department instructor
at Wellesley College last fall, Stephen M. Slivan proved
that small telescopes can yield big discoveries. In fact,
his startling findings were reported in Nature magazine
this fall.
"The science results reported in Nature reveal a
phenomenon that was never before even predicted, namely
that some clusters of asteroids have spin directions that
are correlated," Slivan said. "All prior theories suggest
that they should be random."
The findings have potentially far-reaching impact.
"The main scientific goal is to find clues to help us
understand how our solar system, and Earth in particular,
originally formed and subsequently evolved into what we
see today," Slivan said. "A second aspect of interest is
to study specifically how asteroids break apart in collisions,
which would be a useful thing to know when deciding how
to deal with the future possibility of an Earth-crossing
asteroid someday colliding with our planet."
Slivan says Wellesley's small telescope contributed to
the findings.
"Data I obtained using Wellesley's Whitin Observatory
24-inch telescope last November, only about two weeks after
I began teaching here, are included in the data from which
the results were derived," he said. "The fact that small
telescopes in the Northeast (Wellesley's 24-inch, MIT's
24-inch and Colgate's 16-inch) can produce results meriting
publication in Nature defies the 'common knowledge'
that only big observatories at mountaintop sites can do
world-class research."
Another factor in his study belies another fallacy: that
first-year college students do not contribute to important
research. At Wellesley, they most certainly did.
"Erin Marie Collins, then a first-year student, availed
herself of the opportunities for early involvement in real
research, encouraged and supported by the Astronomy Department
faculty, and directly assisted me in obtaining the Wellesley
data by observing with the 24-inch telescope," Slivan said.
"Our lightcurve from that night appears in the Nature
article. The details of the observing program will appear
in a longer second manuscript currently in review at the
planetary science journal Icarus."
Collins, of Smyrna, Ga., is excited about her contribution.
"At the time, I had no idea that that what I was observing
would be such a big deal," she said. "It's thrilling to
know that I contributed to such a significant project."
Now a sophomore majoring in psychology and minoring in astronomy,
Collins continues to work at the Wellesley observatory using
the 24-inch telescope this fall along with other students.
Here's a summary of Slivan's findings, in his own words:
"My research is a long-term observational study of the
largest members of the Koronis family of asteroids. Asteroids
are small, rocky bodies in the solar system that orbit the
sun and are thought to be bits of material that never formed
into a planet. They offer us clues about the conditions
under which the solar system, including Earth, originally
formed.
"Even though asteroids seem to be primitive material,
we expect that they've not remained completely unchanged
since the solar system originally formed. Collisions between
asteroids have probably played a major role in creating
the asteroids that we see today from larger objects that
existed in the past. When a large asteroid is shattered
and dispersed by a collision, the resulting fragments can
form an 'asteroid family' whose members all have nearly
identical orbits. To some extent we can think of the family
as the outcome of a huge natural collision experiment, much
more energetic than anything that humans have ever experienced.
By studying the sizes, shapes and orientations of the pieces
(that is, the family members) we can better understand what
happened in the collision. The hope is that, eventually,
this knowledge could be applied to the asteroids as a whole
to help figure out how the present asteroid population is
related to the original population.
"One of the most populous of these groupings is the Koronis
family, whose members orbit among the main belt asteroids
between Mars and Jupiter. Determining the shapes and orientations
of Koronis family members from Earth presents a challenge
because they're far enough away that even the largest members
(diameters of about 40 km) are too small to appear as anything
but a small dot of light, just like a faint star. The trick
is to take advantage of the fact that asteroids in this
size range tend to be irregularly shaped, exhibiting a change
in brightness as they rotate and alternately present end-on
and side-on views. A plot of these brightness changes over
time is called a lightcurve. By observing lightcurves of
an object over many years as the viewing geometry changes,
it's possible to get enough data to work backwards and deduce
information about the object's shape, the orientation of
its spin axis and which way it's spinning on that axis.
"Prior to 1992 only a handful of Koronis family lightcurves
had been recorded, far fewer than needed to do shape and
spin solutions. Since that time I've been observing more
lightcurves, and by the summer of 2001 I'd accumulated enough
new data that I could run shape and spin solutions for nine
of the largest members of the Koronis family.
"The results proved to be quite a surprise. Theoretical
models of family formation and laboratory-scale collision
experiments both predict that the tremendous amount of energy
released in a large asteroid collision yields fragments
that randomly spin off into space, but my observations show
that, at least for the Koronis family, the spin axes are
markedly clustered into only two preferred directions. Even
more surprising is that there's an obvious correlation between
the two spin orientations and two preferred rotation rates.
As of now, current understanding of how families form and
evolve has no consistent way to explain how these objects
could possibly be aligned in the way they are. In the Nature
paper, I very briefly speculate that perhaps secondary collisions
after the family-forming collision formed the two observed
'spin clusters,' or perhaps some previously unsuspected
dynamical effect can organize randomly oriented spins into
the observed groupings."
For more on the Wellesley Astronomy Department and Whitin
Observatory, go to www.wellesley.edu/Astronomy/.
The full text of Slivan's article can be found on the
Nature web site at www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v419/n6902/full/nature00993_fs.html.
For a summary published by space.com, go to www.space.com/scienceastronomy/asteroid_siblings_020904.html.
Founded in 1875, Wellesley College has been a leader in
liberal arts and the education of women for more than 125
years. The College's 500-acre campus near Boston is home
to 2,300 undergraduate students.
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